Age-hardening martensitic steels

ABSTRACT

Age-hardening martensitic steel consisting essentially of 0.2% to 0.6% carbon, 4% to 6% chromium, 1% to 2% molybdenum, 0.2% to 0.8% vanadium, 0.25% to 3% aluminum and 2% to 7% nickel.

United States Patent inventor Frank A. Malagari. Jr.

, Freeport. Pa. Appi. No. 818,445 Filed Apr. 22, 1969 Patented Nov. 9, 1971 Assignee Allegheny Ludlum Steel Corporation Pittsburgh, Pa.

AG E-l-IARDENING MARTENSITIC STEELS 4 Claims, No Drawings Primary Examiner- Hyiund Bizot Allorne vs-Richurd A. Specr and Vincent G. Gioiu ABSTRACT: Age-hardening martensitic steel consisting essentialiy of 0.2% to 0.6; carbon, 4% to 6% chromium, 1% to 2% molybdenum. 0.2% to 0.871 vanadium, 0.25% to 3% aluminum and 2% to 7% nickel.

AGE-HARDENING MARTENSITIC STEELS In the past, improvements in tool steels have generally been made by increasing the carbon content'and/or adding carbide forming elements to decrease the hardness and provide improved abrasion resistance. Such alloy modifications have im- 5 min n nickel Sofie" I about 30 f r 3 r men 8! proved tensile properties but at a sacrifice of ductility. In fact 1200 AS the data in table II in ica he yield strength of the workability of such steels has been reduced to such an exthe compositions comamlng "Ickel and aluminum Increases tent that they are very notch sensitive and properties a dif. about 50,000 p.s.1. A tensile strength increase ofabout 22,000 ficult to obtain by testing. p.s.i. is accompanied by a very small change in elongation.

Recem ff to improve too] Steels have been directed to Preferred compositions in accordance with the invention conincorporating age-hardening elements to facilitate aging reac- P 'F P carbon p i to P tions in normal martensitic steels. At first this approach was vanadmm' PF alummun? and 3 tried with high-speed tool steels but was unsuccessful since the Percent such steels may also R maximum hardness attained was the same as that achieved 1 percent smconi some manganese and other mmor alloymg with the base composition. The present invention involves a i z f d th h h composition in which aging response is induced in a hot as 3: t at g g at er L worked die steel. The compositions in accordance with the ingi l z g 'l f 'g j E T ecxeasets 9 i vention contain nickel and aluminum which result in the imer ours a y percen me 8 Is added then the hardness decreases still further. If both aluproved hardness and strength with no apparent loss of 2O minum and nickel are present in the steel maximum hardness toughness. As will be hereinafter discussed in connection with approaching 60 R can be obtained by holding two hours at examples of the preferred embodiments of the invention, it is F I possible by pratcuclzg 2 s prcrwlde an g i i f Mechanical property testing indicates that an improvement room :g we I 5 i i i m i e of45,000 p.s.i. in yield strength and tensile strength can be obstfengt y 0 a 3% a 99" t as ,9 tained in steels containing nickel and aluminum. This immmed that an 8 reaction addfllon to the maftfiflsmc provement will occur if the steel is quenched from l800 F. hardening pp responsible [he Improved P P austenitizing temperature. The strength improvement will not The following examples illustrate practice ol"v the invention be accompanied by a change in elongation or impact strength. with respect to presently preferred embod ments. if hardened at a higher temperature, e.g. 2|OO F., rather than A series of steels of the compositions described in table I 1800" F., an improvement in yield strength of 100,000 p.s.i. were prepared and plate samples thereofwere subjected to the and a tensile strength increase of 70,000 psi. can be treatments described in table ll. achieved. However, this improvement in strength is accompanied by a decrease in ductile properties and impact strength. lclaim: 'lAiiLi-I i I. An age-hardening martensitic steel consisting essentially out No M" s Si Mo M Ni of 0.2 percent to 0.6 percent carbon, 4 percent to 6 percent chromium, 1 percent to 2 percent molybdenum, 0.2 percent R\'1'J4" .25 .30 .000 .004 .31 5.01 1.00 .40 itviisiiiu .25 .104 .004 00:; .30 5. 04 .07 .50 1.04 4.14 to percent vanad'um i to 3 percent aiummum l{\'1618 .30 ,41 .004 00 g5 01; and 2 percent to 7 percent nickel, the balance iron and ii\10'20 .iis 1.30 04 R\'lll48 .41 .0: .003 1.30 resduals' 2. A steel according to claim 1 containing 0.4 percent to 0.6

TABLE 11 (Long) 2% yield 'Iviisiln loi'cvnt CVN Sillpllll'd strength sti'viigth (lOIilZflimpactlrzicturi', Ti'i-iitiiii-iit illdlltSS (p.s.i.) (]).s.i.) tioii (in-lbs.) g. SlZl itviim .25 0,110 Al 01- Ni 1,800" i AC+2 lirs. 000 F. At. 40 10 14 5};

l Al-4 Ni) 1,a00 l -A(+2 lii's. 1,000 F. A(, 54 1 2321, 000 267,400 14 0% 2,100 F--A(1+2 lll'S. 1,000 F. AC 54. 5 c 231,300 64 000 ii 12 0 ,4

18 (.40 llzisi) 1,s00 F.---A(!+2i11-s. nt 1,000 i At 54 i 4 7 s 2,000 F.A(/+2 lil'S. 1it1,00l) l A( (f 243, 2500 250,100 4 7 0 1,875" F. A(-+3 L(l]lI)(l'S at 1,000" l.

RV1620 (.40 (3-1.4 Al-4 Ni) i,s00 F.- -A( 1+2 lll'S. =11. 1,0001 A( 00 (1 288, 600 335,100 7 7 0 2,100 F.-A(I+2l1rs.itt1,000 i A(.. 00 343,100 304,000 1 4 7 RV1948(.40(-0.0Al-4 Ni) 1,8lll)1.'A()+2lllS. aLJUO" l .1 \(l 54.5(1 233,500 315,000 3 17 develops a maximum hardness after 2 hours at l000 F. of

about 540R After a heat treatment at l 100 F. this hardness decreases to 48.5 and continues to decrease to a hardness of 38 R after holding at l200 F. The compositions without alu- 1 Hail sitiiiplo crack in lillvt.

It is apparent in the data in the aforementioned tables that the compositions without aluminum or nickel have a hardness percent carbon.

3. A steel according to claim 1 containing 0.5 percent to L5 of about 48.5 RC after air cooling from 1800 F. and holding 2 percent aluminum.

hours at 900-l000 F. In contrast thereto Heat'RVl6l9 which contains 1 percent aluminum and 4 percent nickel 4. A steel according to claim 1 containing 3 percent to 5 percent nickel. 

2. A steel according to claim 1 containing 0.4 percent to 0.6 percent carbon.
 3. A steel according to claim 1 containing 0.5 percent to 1.5 percent aluminum.
 4. A steel according to claim 1 containing 3 percent to 5 percent nickel. 